Alzheimer's disease (AD) is the most common cause of dementia in the elderly, with more than 4.5 million Americans currently suffering from the disease. Clinical management of AD is complicated by lack of effective methods for early and accurate diagnosis of the disease. Thus, there is a significant unmet need for Alzheimer's disease diagnostic tools. The hypothesis of this project is that single photon emission computed tomography (SPECT) imaging with 123 I-IMPY provides a biomarker for detection of amyloid plaques useful for both 1) Early and definitive diagnosis of AD in the community setting and for 2) Evaluating new therapies targeted and reducing plaque burden in large multi-site clinical trials. To test this hypothesis, a novel 123 I -labeled radiopharmaceutical, 123 I-IMPY, was developed to specifically and sensitively bind A[unreadable] (the chief constituent of amyloid plaques). Working with our collaborators, we have recently demonstrated the safety and biodistribution of this radiopharmaceutical in an initial Phase I clinical trial. In other ongoing clinical trials we are beginning to demonstrate the efficacy of this diagnostic imaging agent, however additional validation work as described in this grant is still required. Thus Phase I of this project will now assess the feasibility and reliability of using this radiopharmaceutical as a biomarker for measuring plaque burden in AD patients. If 123 I-IMPY has suitable clinical properties as a biomarker for measuring amyloid plaques then Phase II will test the characteristics of the biomarker in longitudinal studies of AD and mild cognitive impairment (MCI) patients. Successful accomplishment of these studies will yield an innovative radiopharmaceutical product for the evaluation and diagnosis of AD. A widely available SPECT imaging test for AD will yield significant scientific, commercial and societal benefits. RELEVANCE Successful accomplishment of this Phase I project will result in the validation of 123 I-IMPY as an imaging biomarker for amyloid plaques in AD. Development of such a product will represent a significant technological and scientific innovation that will allow for widespread clinical benefits by facilitating early and accurate diagnosis of AD, using a technique (SPECT imaging) appropriate for the primary care / community medical setting. In addition, it will allow for scientific and technological benefits by improving our understanding of AD and catalyzing the development and evaluation of novel therapies for this devastating disease. [unreadable] [unreadable] [unreadable]